Fentanyl Lidocaine Ketamine CRI Calculator

? 1. Select your CRI setup mode (tab).
2. Enter patient details and select species.
3. Enter mode-specific parameters.
4. Adjust dose rate using the slider.
5. Review calculated drug volumes and rates.
6. Check premed and loading dose recommendations.

Calculator Modes - Which One Should I Use?

• ⭐ Dual Pump (Recommended): Ideal for most clinics. This mode has two options:
  • Standard Fluid Pump: Use two standard fluid pumps. Run the CRI at a constant maintenance rate (typically 3 mL/kg/hr) and add a secondary line intra-operatively for additional fluids (typically +2 mL/kg/hr = 5 mL/kg/hr total). Drug delivery remains constant throughout all phases. This is the most flexible and safest approach.
  • Syringe Driver Pump: Use a syringe driver for highly concentrated, low-volume CRI administration. Ideal for smaller patients or when you need precise, slow infusion rates. The syringe driver delivers only the drugs, while plain maintenance fluids are administered separately via a standard pump (manually adjusted between 3 mL/kg/hr pre/post-op and 5 mL/kg/hr intra-op).
• Single Pump: For clinics with only one fluid pump available. Manually adjust the pump rate between maintenance (3 mL/kg/hr) and surgical rates (5 mL/kg/hr). Drug concentrations are calculated to deliver target doses at the surgical rate, with reduced doses automatically calculated for pre/post-op phases at maintenance rates.
• Flexible Rate: The original calculator mode. Choose your container size and duration, and the calculator determines the required fluid rate. Useful when you want to work backwards from a specific container size.

Important Notes on Drug Concentrations and Administration

• Drug Concentrations: Ensure that your drug concentrations align with those specified in the calculator. This guidance is based on Fentanyl at a concentration of 0.05 mg/mL (50 mcg/mL).
• Patient Weight: The patient's weight is only required for calculating the fluid rate and the loading dose. The amount of drug to be added is determined by the drug dose rate, the fluid administration rate, and the size of the fluid bag.
• Syringe Size: Using 20 or 50 mL syringes is recommended as they require less drug volume and allow for a lower mL/hr administration rate.
• Fluid Rate Calculation: To administer analgesia over an 8-hour period, divide the total fluid volume by 8 to estimate the fluid rate. For example, administering 50 mL over 8 hours corresponds to approximately 6.25 mL/hr. Adjust the fluid rate (indicated in orange) so that it is close to 6 mL/hr.
• Loading Dose: Prepare the loading dose in the same syringe and administer it slowly via IV before any painful procedure, ideally shortly after induction.
• Respiratory Depression: In some patients, the loading dose may cause brief respiratory depression. If this occurs, remain calm. You can stimulate breathing by gently squeezing the philtrum of the nose or by rubbing the chest wall.
• ⚠️ CRITICAL - Diluent Selection for Ketamine CRIs:
  • Use ONLY Normal Saline (0.9% NaCl) as diluent for any CRI containing ketamine.
  • DO NOT use Hartmann's solution (Lactated Ringer's solution) - the calcium ions in Hartmann's solution can cause ketamine to crystallise and precipitate out of solution.
  • This drug incompatibility can result in:
    • Crystal formation visible in the syringe or IV line
    • Reduced bioavailability of ketamine
    • Potential IV line occlusion
    • Unpredictable drug delivery
  • Clinical tip: Always check your diluent before preparing ketamine-containing CRIs. If you notice any cloudiness or precipitation after mixing, discard immediately and remake with normal saline.

Contraindications

1. Fentanyl:
   • Use with caution in animals with respiratory depression or head injuries (can increase intracranial pressure).
   • Avoid in patients with severe liver disease.
   • Note: While MAO inhibitors are rarely used in veterinary medicine, be aware of potential interactions if a patient has been treated with selegiline (used for cognitive dysfunction in dogs) or possibly amitraz (found in some tick collars and dips). These drugs may potentiate the effects of opioids like fentanyl.
2. Lignocaine (Lidocaine):
   • Contraindicated in patients with known hypersensitivity to lignocaine or amide-type local anaesthetics.
   • Use with caution in patients with significant cardiac conditions (e.g., third-degree heart block, severe bradycardia).
   • Reduce dosage in patients with hepatic or renal impairment.
   • Note: The difference between therapeutic and toxic/lethal doses of lignocaine in cats is small. Therefore, lignocaine is not recommended for use in cats and is automatically removed from the calculator for feline patients.
3. Ketamine:
   • Avoid in patients with a history of seizures, increased intracranial pressure, or severe hypertension.
   • Use with caution in cats with hypertrophic cardiomyopathy.
   • Contraindicated in patients with severe thyroid dysfunction or phaeochromocytoma.

Cautionary Notes

• Monitoring: Continuous monitoring of vital signs is crucial:
  • Heart rate and ECG
  • Respiratory rate and effort
  • Blood pressure
  • Oxygen saturation (SpO2)
  • End-tidal CO2 (if available)
  • Temperature (risk of hypothermia with prolonged use)
  Adjust the infusion rate based on the patient's response and monitored parameters.
• Drug Interactions:
  • Use caution when combining with other CNS depressants or anaesthetics.
  • Be aware of potential interactions with other medications the patient may be receiving (e.g., anticonvulsants, antiarrhythmics).
• Patient Selection:
  • Reserve FLK CRI for patients requiring intense pain management (e.g., major surgery, trauma).
  • Consider individual patient factors such as age, breed, and pre-existing conditions.
• Dose Calculations:
  • Double-check all dose calculations and CRI rates before administration.
  • Use lean body weight for dose calculations in obese patients.

Side Effects and Management

1. Fentanyl:
   • Common: Respiratory depression, bradycardia, urinary retention
   • Less common: Dysphoria, agitation
   • Management:
     • Reduce CRI rate or discontinue if severe
     • Administer naloxone in cases of severe respiratory depression
     • Provide oxygen supplementation or ventilatory support if needed
2. Lignocaine (Lidocaine):
   • Watch for signs of toxicity:
     • Dogs: Vomiting, ataxia, lethargy, seizures
   • Management:
     • Discontinue CRI immediately if toxicity is suspected
     • Provide supportive care (airway management, anticonvulsants if needed)
     • Monitor ECG closely
3. Ketamine:
   • At sub-anaesthetic doses, side effects are generally mild
   • May include: Increased salivation, muscle rigidity, transient increases in blood pressure
   • Management:
     • Reduce CRI rate if side effects are problematic
     • Consider adding an anticholinergic for excessive salivation